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https://github.com/rust-lang/rust/issues/65721
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# Motivation
This macro is:
* General-purpose (not domain-specific)
* Simple (the implementation is short)
* Very popular [on crates.io](https://crates.io/crates/matches)
(currently 37th in all-time downloads)
* The two previous points combined make it number one in
[left-pad index](https://twitter.com/bascule/status/1184523027888988160)
score
As such, I feel it is a good candidate for inclusion in the standard library.
In fact I already felt that way five years ago:
https://github.com/rust-lang/rust/pull/14685
(Although the proof of popularity was not as strong at the time.)
Back then, the main concern was that this macro may not be quite
universally-enough useful to belong in the prelude.
# API
Therefore, this PR adds the macro such that using it requires one of:
```
use core::macros::matches;
use std::macros::matches;
```
Like arms of a `match` expression,
the macro supports multiple patterns separated by `|`
and optionally followed by `if` and a guard expression:
```
let foo = 'f';
assert!(matches!(foo, 'A'..='Z' | 'a'..='z'));
let bar = Some(4);
assert!(matches!(bar, Some(x) if x > 2));
```
# Implementation constraints
A combination of reasons make it tricky
for a standard library macro not to be in the prelude.
Currently, all public `macro_rules` macros in the standard library macros
end up “in the prelude” of every crate not through `use std::prelude::v1::*;`
like for other kinds of items,
but through `#[macro_use]` on `extern crate std;`.
(Both are injected by `src/libsyntax_ext/standard_library_imports.rs`.)
`#[macro_use]` seems to import every macro that is available
at the top-level of a crate, even if through a `pub use` re-export.
Therefore, for `matches!` not to be in the prelude, we need it to be
inside of a module rather than at the root of `core` or `std`.
However, the only way to make a `macro_rules` macro public
outside of the crate where it is defined
appears to be `#[macro_export]`.
This exports the macro at the root of the crate
regardless of which module defines it.
See [macro scoping](
https://doc.rust-lang.org/reference/macros-by-example.html#scoping-exporting-and-importing)
in the reference.
Therefore, the macro needs to be defined in a crate
that is not `core` or `std`.
# Implementation
This PR adds a new `matches_macro` crate as a private implementation detail
of the standard library.
This crate is `#![no_core]` so that libcore can depend on it.
It contains a `macro_rules` definition with `#[macro_export]`.
libcore and libstd each have a new public `macros` module
that contains a `pub use` re-export of the macro.
Both the module and the macro are unstable, for now.
The existing private `macros` modules are renamed `prelude_macros`,
though their respective source remains in `macros.rs` files.
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make is_power_of_two a const function
This makes `is_power_of_two` a const function by using `&` instead of short-circuiting `&&`; Rust supports bitwise `&` for `bool` and short-circuiting is not required in the existing expression.
I don't think this needs a const-hack label as I don't find the changed code less readable, if anything I prefer that it is clearer that short circuiting is not used.
@oli-obk
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Rename the default argument 'def' to 'default'
Fixes: #65492
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Remove leading :: from paths in doc examples
Noted some pre-2018 path syntax in the doc examples, for example:
https://doc.rust-lang.org/std/process/fn.exit.html
```rust
fn main() {
::std::process::exit(match run_app() {
Ok(_) => 0,
...
```
Couldn't find an existing issue on this (then again, "::" makes for an annoying thing to search for) so if there is already something fixing this and/or there's a reason to not fix it, just close this PR.
(Also fixed indentation in the `process::exit()` docs)
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Fixes: #65492
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Remove unneeded `ref` from docs
Will reduce confusion like in https://users.rust-lang.org/t/help-understanding-the-ref-t-syntax/33779 since match ergonomics means you (almost) never have to say `ref` anymore!
There might be more like this, but I don't have a checkout on my computer right this second and I'm on slow wifi and GitHub search isn't powerful enough and that's my story.
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Inline `ptr::null(_mut)` even in debug builds
I think we should treat `ptr::null(_mut)` as a constant. As It may help reduce code size
in debug build.
See godbolt link: https://godbolt.org/z/b9YMtD
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Will reduce confusion like in https://users.rust-lang.org/t/help-understanding-the-ref-t-syntax/33779 since match ergonomics means you (almost) never have to say `ref` anymore!
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Fix left/right shift typo in wrapping rotate docs
This makes the note similar to the one found on rotate functions for primitive types like i32/u32.
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properly document panics in div_euclid and rem_euclid
For signed numbers, document that `div_euclid` and `rem_euclid` panic not just when `rhs` is 0, but also when the division overflows.
For unsigned numbers, document that `div_euclid` and `rem_euclid` panic when `rhs` is 0.
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Always inline `mem::{size_of,align_of}` in debug builds
Those two are const fn and do not have any arguments. Inlining
helps reducing generated code size in debug builds.
See also #64996.
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This makes the note similar to the one found on rotate functions for
primitive types like i32/u32.
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fmt::Write is about string slices, not byte slices
No idea why the docs talk about bytes, maybe a copy-paste error?
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add example for type_name
So users of this function could at least expect what its output for current compiler version.
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Move debug_map assertions after check for err
Fixes #65231
We have some assertions in `DebugMap` to catch broken implementations of `Debug` that produce malformed entries. These checks don't make sense if formatting fails partway through. This PR moves those assertions to within the `and_then` closures along with the other formatting logic, so they're only checked if the map hasn't failed to format an entry already.
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- Compatible with Emscripten 1.38.46-upstream or later upstream.
- Refactors the Emscripten target spec to share code with other wasm
targets.
- Replaces the old incorrect wasm32 C call ABI with the correct one,
preserving the old one as wasm32_bindgen_compat for wasm-bindgen
compatibility.
- Updates the varargs ABI used by Emscripten and deletes the old one.
- Removes the obsolete wasm32-experimental-emscripten target.
- Uses EMCC_CFLAGS on CI to avoid the timeout problems with #63649.
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Add `dyn` to `Any` documentation
I noticed that in documentation to `Any` trait the old trait object syntax is used, which could be confusing for newcomers, since we generally recommend using `dyn Trait` instead of just `Trait`. This PR changes the documentation comment, so that it uses `&dyn Any`, `&mut dyn Any` and `Box<dyn Any>`, correspondingly.
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Fix typo in task::Waker
fixes #65323
in `libstd/error.rs` there are a few mentions of `trait@Send` and `trait@Sync`. Are they wrong as well?
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improve performance of signed saturating_mul
Reciprocal throughput is improved from 2.3 to 1.7. https://godbolt.org/z/ROMiX6
Fixes #65309.
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Split non-CAS atomic support off into target_has_atomic_load_store
This PR implements my proposed changes in https://github.com/rust-lang/rust/issues/32976#issuecomment-518542029 by removing `target_has_atomic = "cas"` and splitting `target_has_atomic` into two separate `cfg`s:
* `target_has_atomic = 8/16/32/64/128`: This indicates the largest width that the target can atomically CAS (which implies support for all atomic operations).
* ` target_has_atomic_load_store = 8/16/32/64/128`: This indicates the largest width that the target can support loading or storing atomically (but may not support CAS).
cc #32976
r? @alexcrichton
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Co-Authored-By: Jonas Schievink <jonasschievink@gmail.com>
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I noticed that in documentation to `Any` trait the old trait object syntax is used, which could be confusing for newcomers, since we generally recommend using `dyn Trait` instead of just `Trait`. This PR changes the documentation comment, so that it uses `&dyn Any`, `&mut dyn Any` and `Box<dyn Any>`, correspondingly.
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do not reference LLVM for our concurrency memory model
Fixes https://github.com/rust-lang/rust/issues/65282
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Improve docs on some char boolean methods
simple revival of #61794
(also rustfmt on rest of file :)
Documentation for `is_xid_start()` and `is_xid_continue()` couldn't be improved since both methods got remove from this repository
r? @dtolnay
cc @JohnCSimon
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Reciprocal throughput is improved from 2.3 to 1.7.
https://godbolt.org/z/ROMiX6
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Tracking issue: https://github.com/rust-lang/rust/issues/61129
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Make `Cell::new` method come first in documentation
Methods to create a thing usually comes first in `std` documentation, and `Cell` has been an exception. Also, `T: Copy` specialized methods should not be on top of the page. (This had led me to miss that most of its methods are not bounded by `Copy`...)
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rewrite documentation for unimplemented! to clarify use
The current docs for `unimplemented!` seem to miss the point of this macro.
> This can be useful if you are prototyping and are just looking to have your code type-check, or if you're implementing a trait that requires multiple methods, and you're only planning on using one of them.
You could also return a `()` if you just want your code to type-check.
I think `unimplemented!` is useful for when you want your program to exit when it reaches an unimplemented area.
I rewrote the explanation and gave examples of both forms of this macro that I think clarify its use a little better.
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Revert #63649 - "Upgrade Emscripten targets to use upstream LLVM backend"
This change caused the runtime of the linux-asmjs builder to nearly double from 2+ hours to about 4 hours, which happens to be the bors timeout. (It made it in barely under 4 hours when it was merged.) This is causing timeouts on all new changes.
This reverts commit 7870050796e5904a0fc85ecbe6fa6dde1cfe0c91, reversing
changes made to 2e7244807a7878f6eca3eb7d97ae9b413aa49014.
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Allow unused attributes to avoid incremental bug
cc #65023
This isn't labeled as fixing that issue because it's not really a fix, just a patch.
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